Table 4. Relationships between clinical signs with subtype and season among pigs tested for influenza virus, midwestern United States, June 2009–December 2011*.
| Variable | Estimate | Odds ratio (95% CI) | p value |
|---|---|---|---|
| Season† | |||
| Intercept | –0.234 | NA | 0.65 |
| Fall (referent) | NA | NA | NA |
| Spring | –0.411 | 0.6 (0.1–2.5) | 0.53 |
| Summer | –0.410 | 0.6 (0.1–2.4) | 0.53 |
| Winter |
0.361 |
1.4 (0.3–6.7) |
0.63 |
| Influenza virus subtype‡ | |||
| Intercept | 1.7 | NA | 0.95 |
| H1N1 (referent) | NA | NA | NA |
| H1N2 | –1.381 | 0.5 (0.1–2.0) | 0.96 |
| H3N2 | –1.476 | 0.5 (0.09–2.5) | 0.95 |
| H1N2v | –2.105 | 0.2 (0.03–2.0) | 0.93 |
| H3N2v | 9.541 | NA | 0.95 |
| H1N1pdm09 | –1.582 | 0.4 (0.1–1.7) | 0.95 |
| Mixed infection | –2.210 | 0.2 (0.04–1.3) | 0.93 |
*Logistic regression univariate analysis; NA, not applicable. †Generalized χ2 divided by degrees of freedom = 0.96. ‡Likelihood ratio χ2 (6) = 6.01 df, p = 0.42.